Technology for manipulating digital video has progressed to a point where it can be readily processed and handled on computers. Video production systems have been provided wherein digital video can be readily captured, edited, and displayed for various purposes, such as broadcast television and film and video program post-production.
Typical production systems typically operate in a composition mode, for creating production material, adding special effects and the like. When it is desired to view the results of the composition, the production systems switch to a display mode, where portions of the edited product are displayed for viewing. When generating a composition, the user typically switches between these modes of operation to monitor the quality of decisions made during composition.
One example of such a video production system is described in PCT patent application WO 94/24815, filed Apr. 16, 1993 and entitled "Media Pipeline with Multichannel Video Processing and Playback", incorporated herein by reference. In this system, two streams of video data are independently compressed or decompressed and the results are blended to form a composite image. Processing and keying is performed on the blended data stream.
One advantage of the above system is that it allows different resolutions and compression amounts to be applied to the two data streams. However, the positioning of the blender limited the amount of keying events that could be added to the production on any given pass through the pipeline. In addition, because only two stream of data were processed, often the generation of composite images, which result from a blending of multiple streams of data, required multiple passes through the pipeline.